Breakdown potential control assembly for gas flow-through electrical discharge device

ABSTRACT

An electrical discharge device having a circulating gas medium and which incorporates gas permeable electrode members for permitting increased pumping speed of the circulating gas to thereby reduce the gas pressure while maintaining the desired distance between electrodes to obtain an increase in the breakdown potential.

United States Patent Inventors Charles Herbert Gleason; [56] ReferencesCited George K. Yamasalri, both of llorseheads, UNITED STATES PATENTS AI N $22 3,087,113 4/1963 Foster 315 108x l 91970 3,188,180 6/1965Ho1ler..... 356/86 ux gf 3,361,907 1 1968 Gregory 250/83.6X 3,378,725 41968 Bochinski et al. 315/111 Assignee Westinghouse Electrlc CorporatmnPittsburgh, Pa. FOREIGN PATENTS 967,047 8 1964 Great Britain 356/86Primary ExaminerRoy Lake BREAKDOWN POTENTIAL CONTROL ASSEMBLY AssistantExaminer-Palmer C. Demeo FOR GAS FLOW-THROUGH ELECTRICAL DISCHARGEDEVICE AttorneysF. H. Henson and C. F. Renz 5 Claims, 3 Drawing Figs.

US. Cl 315/108, ABSTRACT: An electrical discharge device having acirculat- 313/209, 315/1 1 1, 356/116 ing gas medium and whichincorporates gas permeable eleclnt. Cl H0 1] 61/10, trode members forpermitting increased pumping speed of the H0lj 61/24 circulating gas tothereby reduce the gas pressure while main- Field of Search 313/210,taining the desired distance between electrodes to obtain an 209;356/86; 315/108, 111; 250/83.6 FT increase in the breakdown potential.

LIGHT OUT V \l/ f 19. 26 22 PUMP OUT 5 :GAS IN PATENTED 0m 5197i 35 I02050|OO2005OO PXd (mm Hg xcm) INVENTORS Charles H Gleason .Y m okn BY f a(U2 A1 10 blyg ATTORNEY Q 0nd George K LIGIHT our was WITNESSES KM 7 9/U o P M U P BREAKDOWN POTENTIAL CONTROLASSEMBLY FOR GAS FLOW-THROUGHELECTRICAL DISCHARGE DEVICE BACKGROUND OF THE INVENTION The presentinvention relates to electrical discharge devices in which a circulatinggas medium is provided within the device. In such structures, it isnormally desired that a low breakdown potential exists between aselected portion of the electrode configuration within the gas mediumwhile the remaining portion of the configuration is such that thebreakdown potential is substantially higher than the selected portron.

Electrical breakdown in gas filled electrical devices is dependent onthe effective spacing between the two surfaces to which an electricalpotential difference is applied and the pressure of the gas between thesurfaces. The breakdown potential versus pressure 1: distancerelationships for various gases and mixtures are generally known anddescribed by a family of curves called the Paschen curves. A typicalcurve is shown in FIG. I of the drawing. The Paschen curve indicatesthat the breakdown will occur most readily at a specific value ofpressure x distance and higher voltages are necessary to initiateelectrical breakdown asthe product ;of pressure .1:

distance becomes less or as the product becomes greater. In

many devices, the desired breakdown surface region operates near theminima of the Paschen curve and the remaining structure normally willoperate to the left of the minima. A decrease in pressure or spacingresults in a higher breakdown potential as to the remaining surfaces ofthe device which is of course the desired result.

In a gas flow type device, a pressure gradient will form between theinput and the exit of the gas system. For a given gas pumping system,the pressure between the electrodes of the device is dependent on thedimensions of spacing. The increase of spacing between the electrodeswill attain a more efficient pumping speed and hence lower values ofpressure but the increase in spacing will reduce breakdown potential.

SUMMARY OF THE INVENTION This invention relates to an electricaldischarge device utilizing a gas flow medium in which a member ofsufficient permeability is utilized between two electrode members ofdifferent potential to permit easy pumping of the gas medium butsufficiently impermeable to still maintain the desired distance spacingand low breakdown by means of the porous member positioned therebetween.BRIEF DESCRIPTION OF THE DRAWINGS For a better understanding oftheinvention, reference may be had to the preferred exemplary embodimentshown in the accompanying drawing, in which:

FIG. I is a graphic illustration of a Paschen-curve Pd versus breakdownpotential for a suitable circulating gas medium such as Argon;

FIG. 2 is a sectional view of a glow discharge type device incorporatingthe teachings of this invention; and

FIG. 3 is another view of FIG. 2 illustrating the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring in detail to FIG. I,there is illustrated a glow discharge type of device, the deviceincludes an anode l0, and a cathode 20. The anode comprises a block 12of a suitable electrically conducting material such as brass having acentral opening 14 therein. An anode extension 16 is also provided whichextends downwardly and is tubular in cross section. The central openingI4 is closed off at the upper portion of the anode by a window 18 andthe window 18 is vacuum sealed to the anode block I2. The centralopeningl4 includes the opening in the anode extension 16. A tubularconduit or opening 22 is provided in the anode block 12 to introduce asuitable gas into the central opening 14. An annular groove 24 isprovided on the lower surface of the anode block 12 surrounding thetubular extension I6 andthe central opening 14. The annular groove orcavity 24 is provided with a conduit 26 for exhausting or pumping outthe gas fromthe device. A suitable gas such as argon is continuallycirculated throughthe device by means of a suitable pumping means.

The cathode 20 is an annular member, 30 of a suitable electricallyconductive material such as brass which is provided with a centralopening 32 and into which the anode extension 16 is inserted. Thespacing between the outer surface of the I tubular extension 16 and theinner surface of the opening 32 is about 0.010 inch even though thespacing can be more or less depending on desired pumping rate and gasflow. The cathode 20 is positioned and spaced from the anode 12 by asuitable insulating spacer 34. The pressure in the systems might varyfrom 2 to 20 torr with a gradient through the system. The pumping cavity24 is provided with a gas permeable member 36 in the form of a mesh of asuitable electrically conductive material such as brass or stainlesssteel or anyiother suitable conducting material. The mesh 36 has a meshopening of about 0.010-0.100 inch and a wire diameter of about0.0l00.l00 inch. The member 36 is positioned to shield the inner surfaceof the cavity 24 within the anode block 12 from the'cathode 20. Themember 36 permits the enhanced pumping speed of the gas through thedevice'while maintaining the distance d between the cathode 20 and theanode 10.

It is possible to utilize a porous plug plate, screening, or perforatedplate members composed of materials of good electn cally conductivematerials or of lesser electrical conductivity such as insulatorsandsemiconductors coated with suitable electrically conductive films orcoatings. The member 36 is also not restricted to the flat parallelconfiguration illustrated but may take on other physical configurationssuch as cylindrical or circular. By controlling the rate of gas flowinginto the device, by properly selecting the position of the pumpingorifices, and by controlling the rate of pumping, a "pressure 1:distance". condition of low breakdown voltage can be made to occur inany region of the device while maintaining good electrical holdofi'properties in other areas where electrical breakdown is undesirable. lnso doing, a discharge can be made to occur only where desired.

In the specific device shown the cathode 20 is provided with a flatplatelike member 40 on which a sample material 42 is provided, and theplate member 40 is sealed to the cathode block 20 by means of an O-ringtype seal. The sample also may be the block 40 itself or an ingot or anyslug with a flat surface. The desired area of discharge is located inthe area of the location of the sample material 42 and glow emission isemitted from this area and the region within the tubular extension Thelight is emitted through the window I8. A typical voltage is suppliedbetweenthe cathode 20 and anode I0 by means of a power supply 44 and atypical voltage is about 200-3000 v. The electrode 36 may operate at anysuitable potential. In the specific device shown, the electrode 36 isconnected to the anode 10. It could'also operate at cathode potential.By the construction illustrated the device is made to provide electricalbreakdown'inthe region of the sample material 42 substantially near theminimum of a curve illustrated in FIG. I. By providing the meshelectrode 36 within the pumping cavity the breakdown potential ismaintained to the left side of the minimum portion of the curve and at ahigher breakdown potential. For example, in the device illustrated thebreakdown potential without the mesh electrode 36 might be of about 900volts while the insertion of the mesh electrode 36 positioned at adistance from the cathode 20 of about 0.070 inch was such as to providea breakdown potential of 2,800 volts.

We claim as our invention:

1. A glow discharge device comprising a first electrode and a secondelectrode, said first and second electrodes spaced apart and insulatedfrom each other, said first and second electrodes comprising firstportions between which an electric discharge is desired and secondportions between which a discharge is undesired, means for circulatinggas between said first and. second electrodes, a gas permeable electrodepositioned between said second portions of said first and secondelectrodes to permit a high circulating rate of said gas between saidfirst and second electrodes while providing breakdown potentialprotection between said second portions of said first and secondelectrodes.

2. A glow discharge device comprising a cathode and anode and spacedapart, means for circulating a gas between said cathode and anode, saidcathode having a centrally located opening, said anode having a tubularextension portion extending into said opening, the active portion ofsaid cathode wherein an electrical discharge is formed to said anodepositioned at the opposite end of said opening with respect to saidanode and facing the end portion of said tubular extension of said anodeand a gas permeable electrode positioned between a part of the inactiveportion of said cathode wherein an electrical discharge is undesired andsaid anode to permit circulation of said gas while increasing thebreakdown potential between said anode and said inactive portion ofsaidcathode.

3. The device in claim 2 in which said cathode member is an annularmember having a surface facing a surface of said anode, an annularcavity defined between a portion of said surface of said cathode and aportion of said surface of said anode and said permeable electrodemember positioned within said annular cavity.

4. The device in claim 2 in which glow discharge occurs between saidactive portion of said cathode and said tubular extension of said anodeand the spectral emission is emitted from the device through the openingin said tubular extension and a communicating opening in said anode,said opening in said anode provided with a window.

5. The device in claim 4 in which said gas follows a path in which itenters said communicating opening in said anode, passes through theopening in said tubular extension, passes through the annular passagebetween the outer surface of said tubular extension and the opening insaid cathode, passes into an enlarged annular cavity formed between saidcathode and anode and then to an exit port, said gas permeable electrodemember positioned within said cavity to modify the breakdown potentialwithin said cavity.

1. A glow discharge device comprising a first electrode and a secondelectrode, said first and second electrodes spaced apart and insulatedfrom each other, said first and second electrodes comprising firstportions between which an electric discharge is desired and secondportions between which a discharge is undesired, means for circulatinggas between said first and second electrodes, a gas permeable electrodepositioned between said second portions of said first and secondelectrodes to permit a high circulating rate of said gas between saidfirst and second electrodes while providing breakdown potentialprotection between said second portions of said first and secondelectrodes.
 2. A glow discharge device comprising a cathode and anodeand spaced apart, means for circulating a gas between said cathode andanode, said cathode having a centrally located opening, said anodehaving a tubular extension portion extending into said opening, theactive portion of said cathode wherein an electrical discharge is formedto said anode positioned at the opposite end of said opening withrespect to said anode and facing the end portion of said tubularextension of said anode and a gas permeable electrode positioned betweena part of the inactive portion of said cathode wherein an electricaldischarge is undesired and said anode to permit circulation of said gaswhile increasing the breakdown potential between said anode and saidinactive portion of said cathode.
 3. The device in claim 2 in which saidcathode member is an annular member having a surface facing a surface ofsaid anode, an annular cavity defined between a portion of said surfaceof said cathode and a portion of said surface of said anode and saidpermeable electrode member positioned within said annular cavity.
 4. Thedevice in claim 2 in which glow discharge occurs between said activeportion of said cathode and said tubular extension of said anode and thespectral emission is emitted from the device through the opening in saidtubular extension and a communicating opening in said anode, saidopening in said anode provided with a window.
 5. The device in claim 4in which said gas follows a path in which it enters said communicatingopening in said anode, passes through the opening in said tubularextension, passes through the annular passage between the outer surfaceof said tubular extension and the opening in said cathode, passes intoan enlarged annular cavity formed between said cathode and anode andthen to an exit port, said gas permeable electrode member positionedwithin said cavity to modify the breakdown potential within said cavity.